Several tech-company execs, including Facebook CEO Mark Zuckerberg, signed a letter in support of the FCC’s proposed net-neutrality rules.

“We believe a process that results in common sense baseline rules is critical to ensuring that the Internet remains a key engine of economic growth, innovation and global competitiveness,” a group of 24 CEOs and Internet company founders wrote in a letter to be delivered to the FCC Monday in support of the proposed net-neutrality rules.

“An open Internet fuels a competitive and efficient marketplace, where consumers make the ultimate choices about which products succeed and which fail. This allows businesses of all sizes, from the smallest start-up to larger corporations, to compete, yielding maximum economic growth and opportunity,” they wrote.

Julius Genachowski’s first major act as FCC Chairman kicks off Thursday, when the agency is scheduled to release details of its proposed net-neutrality rules. Both sides of the debate will then have months — many months, from what we’re hearing — to tell the agency what they think of the proposed rules and how they should be changed (or not).

Phone and cable companies are concerned that the FCC proposal could harm their business, and their lobbyists have been pulling out the stops in an effort to soften some of the language.

The pro-net-neutrality coalition of companies formally adds a few new members with the letter, including Twitter and Facebook, which haven’t heavily engaged in policy debates before.

Notably, a few non-Internet companies also signed the letter, including Stan Glasgow, president of Sony Electronics, and Charlie Ergen of satellite-TV provider EchoStar. Ergin isn’t an obvious signatory on such a letter until you consider EchoStar owns Sling Media, the TV-on-the-Internet service which has had a few problems with its iPhone App being blocked from using AT&T’s 3G network. That sort of blocking wouldn’t likely be allowed under the FCC’s net-neutrality proposal.